Kataoka M, Nishii I, Fujisawa T, Ueki T, Tokunaga F, Goto Y
Department of Earth and Space Science, Faculty of Science Osaka University, Japan.
J Mol Biol. 1995 May 26;249(1):215-28. doi: 10.1006/jmbi.1995.0290.
Compactness and shape are two of the critical properties that describe the degree of protein folding. Solution X-ray scattering is an effective technique for measuring these properties quantitatively. Structural characteristics of various conformational states of horse myoglobin were studied in terms of size and shape by solution X-ray scattering. The radius of gyration for native holomyoglobin was 17.5 A, while that of the apomyoglobin native state was 19.7 A. Corresponding to the increase in the radius of gyration, the largest dimension of the molecule also increased from 47.5 A to 62.5 A. Both states are globular in shape. The scattering profiles in the high angle region suggest that the apomyoglobin native state has a distinct tertiary structure, and that packing of alpha-helices in the apomyoglobin native state would be looser than that of holomyoglobin. These observations indicate that the native state of apomyoglobin is expanded from that of holomyoglobin, and that the conformations of the two are not identical. The radii of gyration for the acid-unfolded state and the denaturant-unfolded state were 30 A and 35 A, respectively. Both unfolded states have chain-like conformations without any tertiary structures. The radius of gyration and the largest dimension of the molten globule stabilized by trichloroacetate were 23.1 A and 72.5 A, respectively. The molten globule is expanded from the native state although it is globular, and is much more compact than the unfolded state. The bimodal distance distribution function and scattering profile at high-angle region suggest that the structure of the apomyoglobin molten globule contains a core comprising a cluster of multiple alpha-helices and flaring tail(s), which would be a common structural property of the compact denatured state appearing during the folding process. The compactness of each conformational state is highly correlated with the extent of formation of the alpha-helix.
紧密性和形状是描述蛋白质折叠程度的两个关键特性。溶液X射线散射是定量测量这些特性的有效技术。通过溶液X射线散射，从尺寸和形状方面研究了马肌红蛋白各种构象状态的结构特征。天然全肌红蛋白的回转半径为17.5 Å，而脱辅基肌红蛋白天然状态的回转半径为19.7 Å。与回转半径的增加相对应，分子的最大尺寸也从47.5 Å增加到62.5 Å。两种状态均为球状。高角度区域的散射曲线表明，脱辅基肌红蛋白天然状态具有独特的三级结构，并且脱辅基肌红蛋白天然状态下α-螺旋的堆积比全肌红蛋白的更松散。这些观察结果表明，脱辅基肌红蛋白的天然状态比全肌红蛋白的更伸展，并且两者的构象并不相同。酸变性状态和变性剂变性状态的回转半径分别为30 Å和35 Å。两种变性状态均具有链状构象，没有任何三级结构。三氯乙酸稳定的熔球态的回转半径和最大尺寸分别为23.1 Å和72.5 Å。熔球态虽然是球状，但相对于天然状态是伸展的，并且比变性状态紧凑得多。双峰距离分布函数和高角度区域的散射曲线表明，脱辅基肌红蛋白熔球态的结构包含一个由多个α-螺旋簇组成的核心和向外展开的尾部，这将是折叠过程中出现的紧密变性状态的一个共同结构特性。每个构象状态的紧密性与α-螺旋的形成程度高度相关。
